1. Field of the Invention
The present invention generally relates to charged-particle beam exposure, and more particularly to charged-particle beam exposure in which charged-particle beams are controlled so as to have a desired beam shape as a whole while a stage mounting a sample is continuously moved and the sample is exposed by a raster scan in which the charged-particle beams are deflected by deflectors.
Recently, integrated circuits have been widely applied to industries such as computers, communications and mechanical controls with improvements in the integration density and functions. For example, the integration density of dynamic random access memories (DRAMs) is drastically increased in the order of 1 Mbits, 4 Mbits, 16 Mbits, 64 Mbits, 256 Mbits and 1 Gbits. Such a drastic increase in the integration density is mainly accomplished by advance in precision production techniques. With an increase in the integration density, an exposure system using a charged-particle beam such as an electron beam has been developed as a means for forming fine patterns. The charged-particle beam exposure is capable of realizing fine production equal to or less than 0.05 .mu.m with a positioning precision of 0.02 .mu.m or less. However, it was considered that the throughput of the charged-particle beam is too low to be practically used to produce LSI devices in commercial quantity. The above consideration is based on a theory of drawing with so-called single-strokes of the electron beam and is not a serious consideration. The above consideration was given taking into account only the currently marketed devices and productivity.
Recently, the inventors have proposed a block exposure method and an exposure method using a blanking aperture array. With these exposure methods, it has been expected to realize a throughput as high as 1 cm.sup.2 /sec. The proposed exposure methods are superior to the other conventional exposure methods in terms of fine productivity, positioning precision, quick-turn-around performance and reliability.
The proposed exposure methods are required to efficiently process exposure pattern data and improve exposure throughput as in the case of the other conventional exposure methods.
2. Description of the Prior Art
FIG. 1 shows an exposure pattern data process used in a conventional electron beam exposure system which is one of the charged-particle beam exposure systems. For each chip formed on a wafer, an exposure area is partitioned into main deflection fields within each of which an electron beam can be deflected by main deflectors (electromagnetic deflectors). Each of the main deflection fields are segmented into sub deflection fields within each of which the electron beam can be deflected by sub deflectors (electrostatic deflectors). Exposure pattern data is produced for each of the sub deflection fields.
FIG. 2 shows an exposure area segmented into the main deflection fields and the sub deflection fields in the above-described manner. In FIG. 2, areas defined by thick solid lines are the main deflection fields, and areas defined by thin solid lines are the sub deflection fields. As shown in FIG. 2, the main and sub deflection fields are segmented at respective approximately equal intervals.
In the conventional exposure pattern data process shown in FIG. 1, pattern data is produced for each of the sub deflectors, and does not take into account the natures of exposure patterns, such as repetition of exposure pattern at all. For example, it will now be considered that patterns P1 and P2 shown in FIG. 3 are repeatedly drawn by exposure. Data of the patterns P1 and P2 are produced for each sub deflection field. Hence, exposure patterns located on the boundaries between the adjacent sub deflection fields are divided into a plurality of exposure patterns. For example, the pattern P1 located on the right of the illustration is divided into three patterns. This means that the original pattern P1 is drawn by combining the pattern data of the divided exposure patterns. In practice, a so-called margin area is set around each sub deflection field, and pattern located within the margin area is not allowed to be divided. If the pattern P1 is located within a sub deflection field, it is not divided.
As described above, in practice, different pattern data are needed to draw the same patterns, although the same patterns can be originally drawn by single pattern data. It can be seen from the above that the conventional exposure pattern data process does not produce pattern data taking into consideration the repetition of patterns and needs a large amount of data processing. As the amount of pattern data to be processed increases, the time necessary to transfer pattern data increases. This degrades the throughput of the whole system.
Further, it is liable that a positional deviation of the divided parts forming a single pattern may occur because the single pattern is drawn by separately drawing these divided parts.